1. Field of the Invention
This invention relates to digital signal transmitting systems, and is more particularly directed to a transmission system in which a digital signal is distributed among a plurality of transmission paths. Specifically, this invention involves error correction encoding of a digital signal to be transmitted on a plurality of distribution paths, favorably by means of recording the signal on plural tracks of a recording medium.
2. Description of the Prior Art
One method of encoding a digital signal for error correction and protection from so-called burst errors (such as drop out in the case of a recorded signal) has been proposed in our application Ser. No. 218,256, filed Dec. 19, 1980, issued on Oct. 19, 1982 as U.S. Pat. No. 4,355,392. This method involves rearranging or "interleaving" the words of the digital signal prior to transmission or recording, and then "de-interleaving" or restoring the received or reproduced signal back to its original arrangement. This technique has the advantage of distributing any drop out or burst errors over a large number of the original blocks of the digital signal, so that the correctability of the erroneous words is improved. This prior proposed method more particularly involves a cross-interleaving technique in which PCM data sequences are interleaved two or more times. In such cross-interleaving method the data words are grouped into a plurality of different error correcting code blocks, and each data word relates to several error correcting words. Thus, this technique is rather powerful for correcting burst errors.
Stationary-head, plural track, digital audio tape recording machines have also been previously proposed. In such machines, a plurality of parallel longitudinal tracks are formed on a magnetic tape, and a multi-channel digitized audio signal is recorded thereon. In order to enable the recorder to operate at a reduced speed and to minimize tape consumption, an audio PCM (pulse-code modulated) signal representing a single channel is distributed to several of the plurality of tracks and is recorded thereon.
In such a stationary-head recorder, the above cross-interleaving technique can be used to advantage to improve the correctability of burst errors. However, because the PCM signal is distributed among several tracks, a problem arises in that a burst error extending across two or more of the tracks (e.g., caused by fingerprints or dirt on the tape) can impair the error correctability. Furthermore, correctability of random errors may not be the same for all tracks, but may undesirably vary from track to track.